In cellular systems normally the base-stations transmit wideband pilots, e.g., in every sub-frame, for channel estimations as well as for RSSI (Received Signal Strength Indication) measurements. The handover related measurements are traditionally done by the User Equipment (UE) devices, e.g., wireless terminals such as cell phones. In normal cellular systems, UEs perform measurements on the received pilot signals and report the RSSI measurements of a candidate base station for handover to the serving base station. The working assumptions of such designs are that the base stations are deployed in a planned fashion, the base stations are always transmitting, and that the number of UEs is much larger than the number of base stations. However with the deployment of small base stations (also referred to as small cells) in various systems such assumptions are not always valid.
It is envisioned that the future cellular systems will have a dense and unplanned deployment of the small cells. With dense and unplanned deployment of small base stations with small coverage areas, it is not efficient that the small cells transmit pilots in each sub-frame as it causes pilot pollution (e.g., interference between pilot signals). Pilots of the small cells interfere with each other and are interfered by traffic from active small cells and macro cells. This may result in erroneous RSSI measurements made by UEs.
When the number of UEs in a region is comparable to or less than the number of small cells, many small cells are often not in communications with a UE, i.e., many small cells will not have a UE attached to them most of the time. The pilot transmissions by such small cells can cause interference to active small cells' transmissions, e.g., the transmissions by small base stations which have active UEs attached to them. Furthermore, the pilot transmissions also increase power consumption of the small cells as compared to the amount of power which would be required if such transmission did not have to be made.
While under some conditions, the number of small cells in an area may outnumber the number of UE's in an area, this may not always be the case and may change with time.
From the above discussion, it should be appreciated that there is a need for methods and/or apparatus for dynamically allocating resources for pilot transmissions which results in efficient utilization of resources for pilot signal transmissions.